In the related art, a backlight including a plurality of light emitting diode (LED) elements is generally used as an electronic component configured to illuminate a liquid crystal display from a back surface thereof. Furthermore, there are edge light type and direct type systems as such a backlight, and an edge light type is used for a small liquid crystal used for a portable terminal or the like, a laptop type personal computer, a liquid crystal monitor, and the like.
In an edge light type backlight, a plurality of LED elements are arranged in any lateral surface of a plate-like light guide plate and the entire surface of a liquid crystal panel is irradiated with light through the light guide plate. Since the number of required LED elements is smaller in such a type than that of a direct type, the edge light type backlight has advantages such as low cost, energy saving, and a liquid crystal display which can be made thin.
In recent years, an edge light type backlight is required to be thinner than in the related art, and molding processing used to make a plate-like light guide plate to 0.3 mm or less or an LED element with a thickness of 0.3 mm is being developed.
In the related art, in order to arrange a plurality of LED elements for a backlight, a method for soldering the LED elements in a printed board using a solder material is mainly performed. However, such a method has a limitation on further thinning of the backlight.
FIGS. 7(a) and (b) are diagrams showing a configuration of a light emitting device 101 according to the related art. As shown in FIG. 7(a), the light emitting device 101 includes a printed board 102 and a plurality of LED elements 103. Furthermore, as shown in FIGS. 7(a) and (b), each of the LED elements 103 includes a base part 131, a light emitting unit 132, a positive electrode 133, and a negative electrode 134.
The light emitting unit 132 constituted of a light emitting diode is provided in a first surface of the base part 131. In addition, the positive electrode 133 and the negative electrode 134 are provided in a second surface which is perpendicular to the first surface of the base part 131. In each of LED elements 103, the positive electrode 133 and the negative electrode 134 are connected to the wiring 121 using a solder material 122 to be mounted in the front surface of the printed board 102.
However, like in the light emitting device 101 illustrated in FIGS. 7(a) and (b), since a thickness of a printed board 102, a thickness of the wiring 121, a floating thickness of a joint using the solder material 122, and a thickness of a space required for assembly of the printed board 102 and the resin casing 105 are required in a configuration in which the LED elements 103 are mounted in the front surface of the printed board 102, there is a problem in that a height (thickness in an H direction) of the light emitting device 101 is obtained by adding a thickness of at least about 0.1 mm to a thickness of the LED element 103.
As a countermeasure against such a problem, the light emitting device 101a of a configuration illustrated in FIGS. 8(a) and (b) can be considered.
FIGS. 8(a) and (b) are diagrams showing a configuration of a light emitting device 101a according to the related art. In the light emitting device 101a illustrated in the drawing, the positive electrode 133 and the negative electrode 134 are provided in an opposite side to the light emitting unit 132 of the LED element 103 and connected to the wiring 121 in the printed board 102 via a solder material 104. Since a height (thickness in an H direction) of the printed board 102 is substantially the same as a height of the LED element 103 in such a configuration, a thickness of the light emitting device 101a can be made as thin as a thickness of the LED element 103.
FIG. 8 is a diagram showing a configuration of a light emitting device 101a according to the related art. In the light emitting device 101a illustrated in the drawing, the positive electrode 133 and the negative electrode 134 are provided in an opposite side to the light emitting unit 132 of the LED element 103 and connected to the wiring 121 in the printed board 102 via a solder material 104. Since a height (thickness in an H direction) of the printed hoard 102 is substantially the same as a height of the LED element 103 in such a configuration, a thickness of the light emitting device 101a can be made as thin as a thickness of the LED element 103.
However, in order to realize the light emitting device 101a with such a configuration, it is necessary to prepare the printed board 102 with a narrow width such as 0.3 mm. Since processing of obtaining such a printed board 102 is very difficult, there is a problem regarding an increase in manufacturing costs of the light emitting device 101a. In addition, since a connection area between the LED element 103 and the printed board 102 is decreased, there is also concern that a mounting strength of the LED element 103 will be insufficient.
In addition, miniaturization of a light emitting device is required due to an increasing demand for miniaturization and thinning of electronic devices in recent years. However, in the light emitting device 101 (101a) obtained through a mounting method using the solder material 122 in the related art, it is necessary to secure an installation space of the solder material 122 in the light emitting device 101 (101a) in view of wet spreading of the solder material 122, securing a mounting strength, or the like. Therefore, there is a limit to miniaturization of the light emitting device 101 (101a).
Thus, in the related art, various proposals have been provided as countermeasures to deal with positional deviation of an LED at the time of surface mounting using a solder material.
Patent Literature 1 discloses a method for fixing an LED mounting position by forming a groove in the LED mounting position in a printed board and inserting an LED member joined to a dummy having a dimension which is the same as a mounting pitch of an LED into the groove.
Patent Literature 2 discloses a method for fixing an LED mounting position by putting an adhesive into a hole formed in a printed board, mounting an LED above the adhesive, and curing the adhesive.
Patent Literature 3 discloses a method for fixing an LED mounting position by assembling an LED and a positioned member and then soldering the LED to a circuit of a printed board.